1. Field of the Invention
The present invention relates to an optical measuring apparatus for optically measuring physical quantities such as magnetic field, pressure and electric field.
2. Description of the Prior Art
Referring now to FIG. 1 which is a block diagram showing, for example, a magnetic-field measuring apparatus for measuring the magnetic field of the conventional optical measuring apparatus, reference number 1 designates a light source, 2 designating a transmission path (hereinafter referred to as an optical fiber) formed of an optical fiber connected with the light source 1 at one end thereof for transmitting a light from the light source 1, 3 designating a self-focusing lens mounted on the other end of the optical fiber 2 for changing beams of light radiated from the optical fiber 2 to parallel beams of light, 4 designating a polarizer for changing the parallel beams of light obtained by the self-focusing lens 3 to a linearly polarized light, and 5 designating a magnetic optical element arranged in a magnetic field to be measured for rotating a plane of polarization of the linearly polarized light from the polarizer 4 in correspondence to the magnetic field to be measured. In addition, 7 designating an analyzer for dividing the optical output from the magnetic optical element 5 into polarized ingredients meeting at right angles to each other, 8a, 8b designating lenses for collecting the lights having been divided by the analyzer 7 and making them incident upon optical fibers 9a, 9b, 10a, 10b designating photo-detectors mounted on one end of the optical fibers 9a, 9b for converting the lights transmitted by the optical fibers 9a, 9b into electric signals i1, i2, 11 designating an adder for adding the electric signals i1, i2 having been converted by the photo-detectors 10a, 10b, 12 designating a subtracter for subtracting the electrical signal i2 from the electric signal i1, and 13 designating a divider for dividing the output from the subtracter 12 by the output from the adder 11.
Next, the operation is described. A light radiated from the light source 1 is transmitted by the optical fiber 2, changed to parallel beams of light by the self-focusing lens 3, and converted into the linearly polarized light by the polarizer 4. This linearly polarized light is incident upon the magnetic optical element 5 to rotate the plane of polarization thereof in correspondence to the magnetic field to be measured. The light, whose plane of polarization is rotated, is divided into two polarized ingredients, P.sub.p, P.sub.s meeting at right angles to each other by the analyzer 7 arranged at an angle of 45.degree. to the linearly polarized light of the output from the polarizer 4. The divided lights P.sub.p, P.sub.s are collected by the lenses 8a, 8b and incident upon the photo-detectors 10a, 10b through the optical fibers 9a, 9b to be photoelectrically converted, respectively. An optical strength of the divided lights P.sub.p, P.sub.s is expressed as follows, respectively: EQU P.sub.p =1/2.multidot.P.sub.o (1+sin 2.theta..sub.F) EQU P.sub.s =1/2.multidot.P.sub.o (1-sin 2.theta..sub.F)
wherein .theta..sub.F is an angle of rotation of the plane of polarization by the magnetic optical element 5; and P.sub.o is a strength prior to the incidence upon the analyzer 7.
(P.sub.p -P.sub.s)/(P.sub.p +P.sub.s)=sin 2 .theta..sub.F is derived from the above described equations, whereby the angle of rotation of the plane of polarization can be calculated by a simple operation without using the strength of light. In such an operation (i1+i2) is calculated by the adder 11, (i1-i2) being calculated by the subtractor 12, and (i1-i2)/(i1+i2) being calculated by the divider 13 to determine the angle of rotation of the plane of polarization.
The above described is an example of the conventional magnetic field measuring apparatus, in which the pressure and electric field can be measured by using a photoelastic element and a Pockels element in place of the magnetic optical element 5 in the same construction.
Since the conventional optical measuring apparatus have the above described construction, it is necessary to use a plurality of transmission paths (optical fibers 9a, 9b) between the analyzer 7 and the photo-detectors, whereby the problem has occurred in that a difference in optical loss and a fluctuation in optical loss between a plurality of transmission paths lead to errors of measurement and the like.